Fix the "default arch" code path with Julia nightly (and add a CI job for that code path) (#115)

.github/workflows/checkin.yml

@@ -1,9 +1,16 @@
 name: "PR Checks"
 on: [pull_request, push]
 
+concurrency:
+  # Skip intermediate builds: all builds except for builds on the `master`, `main`, or `release-*` branches
+  # Cancel intermediate builds: only pull request builds
+  group: ${{ github.workflow }}-${{ github.ref }}-${{ github.ref != 'refs/heads/master' || github.ref != 'refs/heads/main' || startsWith(github.ref, 'refs/heads/release-') || github.run_number }}
+  cancel-in-progress: ${{ startsWith(github.ref, 'refs/pull/') }}
+
 jobs:
   check_pr:
     runs-on: ubuntu-latest
+    timeout-minutes: 60
     steps:
     - uses: actions/checkout@v1